This invention relates in general to electrophotography and, more specifically, to a novel photoconductive device and process for using the device.
A photoconductive layer for use in electrophotography may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. One type of composite photoconductive layer used in electrophotography is illustrated in U.S. Pat. No. 4,265,990 which describes a photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer.
Various combinations of materials for charge generating layers (CGL) and charge transport layers (CTL) have been investigated. For example, the photosensitive member described in U.S. Pat. No. 4,265,990 utilizes a charge generating layer in contiguous contact with a charge transport layer comprising a polycarbonate resin and one or more of certain diamine compounds. Various generating layers comprising photoconductive layers exhibiting the capability of photogeneration of holes and injection of the holes into a charge transport layer have also been investigated. The charge generation layer may comprise a homogeneous photoconductive material or particulate photoconductive material dispersed in a binder. Other examples of homogeneous and binder charge generation layer are disclosed, for example, in U.S. Pat. No. 4,265,990. Additional examples of binder materials such as poly(hydroxyether) resins are taught in U.S. Pat. No. 4,439,507. The disclosures of the aforesaid U.S. Pat. No. 4,265,990 and U.S. Pat. No. 4,439,507 are incorporated herein in their entirety. Photosensitive members having at least two electrically operative layers as disclosed above provide excellent images when charged with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. Where polymers such as vinyl hydroxy ester or vinyl hydroxy amide polymers are utilized in adjacent charge blocking layers, poor adhesion is encountered and an additional intervening adhesive is often desirable. Also, when some binder materials are employed in a blocking layer or charge generating layer, the binder can be attacked by some of the solvents employed to apply subsequent layers. Solvent attack of an underlying layer such as the blocking layer cannot normally be tolerated in precision copiers, duplicators, and printers.